This invention is directed to a seat belt retractor mechanism which is particularly useful in a passive retraint type of system which includes a retractor mechanism mounted in a door of a vehicle. A sudden opening of the door will cause the inertia locking retractor to automatically lock and thereby prevent the seat belt from unwinding as intended during the door swinging movement whereby the door movement is abruptly halted because of the stopping of the seat belt unwinding movement. A number of proposals have been suggested for blocking operation of the inertia mechanism and the locking mechanism so that the seat belt may continue to be paid out even though the door is accelerated at a G-force which would operate the inertia locking mechanism. For instance, mechanically spring biased plungers are movable upon opening of the door to operate linkages extending in the door to the retractor mechanisms, but such plunger operated linkages are too slow in operation. Also it has been suggested to use a solenoid device to block the retractor's inertia operated locking mechanism with the solenoid being energized upon electrical contacts closing as the door is opened. Such solenoid devices use electrical power and, if the door remains open for a long period of time there will be a considerable drain on the battery. It will be appreciated that it is preferred that the electrical operation be kept to a minimum period of time so as not to be a burdensome drain on the vehicle battery or electrical system.
When the inertia operated retractor is mounted in a door, it is desirable that it be blocked out from locking from the normal locking force level, e.g., 0.6 or 0.7G to a higher locking force level, e.g., of 3 or 4 G's. That is, at very high loads of 3 or 4 G's or above it, it is desirable from a fail-safe operation that the locking retractor lock the belt against protraction to assure that the passenger will always be protected. The fast swinging of the door will only generate 0.7G or slightly above and should not generate inertia forces of the magnitude of the higher level. Any such block out system should not be the source of electrical drain on the vehicle's battery whether the vehicle door is opened or closed for long periods of time.